Location of the Energy Levels of the Rare-Earth Ion in BaF2 and CdF2

The location of the energy levels of rare-earth (RE) elements in the energy band diagram of BaF2 and CdF2 crystals is determined. The role of RE3+ and RE2+ ions in the capture of charge carriers, luminescence, and the formation of radiation defects is evaluated. It is shown that the substantial difference in the luminescence properties of BaF2:RE and CdF2:RE is associated with the location of the excited energy levels in the band diagram of the crystals

NMR and dc-susceptibility studies of NaVGe2O6

We report the results of measurements of the dc magnetic susceptibility chi(T) and of the 23Na nuclear magnetic resonance (NMR) response of NaVGe2O6, a material in which the V ions form a network of interacting one-dimensional spin S=1 chains. The experiments were made at temperatures between 2.5 and 300 K. The chi(T) data suggest that the formation of the expected low-temperature Haldane phase is intercepted by an antiferromagnetic phase transition at 18 K. The transition is also reflected in the 23Na NMR spectra and the corresponding spin-lattice relaxation rate 1/T1(T). In the ordered phase, 1/T1(T) decreases by orders of magnitude with decreasing temperature, indicating the formation of a gap of the order of 12 K in the magnetic excitation spectrum.Comment: 10 pages, 15 figures; v2 with minor revisions of the tex

Progress on the Development of an Iodine-fed Hall Effect Thruster

The paper deals with the results of an ongoing activity carried out by the Department of Civil and Industrial Engineering (DICI) and the Department of Chemistry and Industrial Chemistry (DCCI) of the University of Pisa (UniPi) in collaboration with SITAEL SpA, aimed at the development of technologies for Iodine-fed Hall Effect Thrusters. A feeding system architecture is described and the results of reduced order numerical models of the feeding system are illustrated, in both steady and unsteady state conditions. An activity for iodine interaction with materials is in progress. The experimental setups for material characterization tests are described. Material samples can be heated from room temperature up to 300 °C and exposed to iodine at high (soakage test) or low (flow test) concentration, simulating the condition at which the materials will undergo in the propulsion system, in the vacuum facility or in the spacecraft. Calibration and preliminary soakage test results are illustrated. On the thruster unit side, the candidate thruster and cathode are presented along with the modifications needed to operate them on iodine. Finally, a description of the foreseen test campaign and associated facilities is presented

Unconventional Charge Ordering in Na0.70CoO2 below 300 K

We present the results of measurements of the dc-magnetic susceptibility chi(T) and the 23Na-NMR response of Na_{0.70}CoO_{2} at temperatures between 50 and 340 K. The chi(T) data suggest that for T > 75 K, the Co ions adopt an effective configuration of Co^{3.4+}. The 23Na-NMR response reveals pronounced anomalies near 250 and 295 K, but no evidence for magnetic phase transitions is found in chi(T). Our data suggest the onset of a dramatic change in the Co 3d-electron spin dynamics at 295 K. This process is completed at 230 K. Our results maybe interpreted as evidence for either a tendency to electron localization or an unconventional charge-density wave phenomenon within the cobalt oxide layer, CoO_2, 3d electron system near room temperature.Comment: 4 pages, 4 figures, re-submitted to Physical Review Letters. The manuscript has been revised following the recommendations of the referees. The discussion section contains substantial change

Lymphocyte reconstitution following autologous stem cell transplantation for progressive MS

BACKGROUND: Autologous stem cell transplantation (ASCT) for progressive multiple sclerosis (MS) may reset the immune repertoire. OBJECTIVE: The objective of this paper is to analyse lymphocyte recovery in patients with progressive MS treated with ASCT. METHODS: Patients with progressive MS not responding to conventional treatment underwent ASCT following conditioning with high-dose cyclophosphamide and antithymocyte globulin. Lymphocyte subset analysis was performed before ASCT and for two years following ASCT. Neurological function was assessed by the EDSS before ASCT and for three years post-ASCT. RESULTS: CD4+ T-cells fell significantly post-transplant and did not return to baseline levels. Recent thymic emigrants and naïve T-cells fell sharply post-transplant but returned to baseline by nine months and twelve months, respectively. T-regulatory cells declined post-transplant and did not return to baseline levels. Th1 and Th2 cells did not change significantly while Th17 cells fell post-transplant but recovered to baseline by six months. Neurological function remained stable in the majority of patients. Progression-free survival was 69% at three years. CONCLUSION: This study demonstrates major changes in the composition of lymphocyte subsets following ASCT for progressive MS. In particular, ablation and subsequent recovery of thymic output is consistent with the concept that ASCT can reset the immune repertoire in MS patients

Effect of Na content and hydration on the excitation spectrum of the cobaltite Na_xCoO_2 yH_2O

We report on a Raman scattering study on the superconducting cobaltite $Na_xCoO_2\cdot yH_2O$ as function of Na content and hydration (x$\approx$1/3, 3/4 and y$\approx$0, 2/3, 4/3). The observed phonon scattering and scattering continua are analyzed in terms of lattice strain due to the structural misfit and disorder. Hydration, due to the intercalation of one or two $H_2O$ layers, releases a part of this strain. Our Raman data suggest a connection between disorder on the partly occupied Na sites, the split off of the $a_{1g}$ level from the other $t_{2g}$ states of $Co^{4+}$ and superconductivity.Comment: 10 pages, 4 figures, for further information see http://www.peter-lemmens.d

Can Energetic Terahertz Pulses Initiate Surface Catalytic Reactions on the Picosecond Time Scale?

In preparation for picosecond pump-probe experiments at the SwissFELX-ray laser facility, the feasibility of collectively initiating surface chemical reactions using energetic pulses of terahertz radiation is being tested

Integração da simulação termoenergética nas primeiras fases do processo projetual: o estudo de seis casos

Resumo O artigo tem o objetivo de demonstrar a viabilidade de integração de simulações termoenergéticas ao processo projetual desde as primeiras fases do projeto. Para tanto, apresenta uma sistematização dos procedimentos entre projetista e simulador para seis estudos de caso de edificações em clima quente. Destaca-se a necessidade de compreensão das características do edifício e da programação arquitetônica, incluindo informações, metas e necessidade, além de partido e intenções da solução, que motivaram a montagem de um checklist para melhorar o diálogo entre simulador e projetista. Os resultados também apontam as características da edificação que mais influenciam no consumo energético da edificação, e a interação entre o simulador e o projetista, de acordo com seu perfil, as liberdades e restrições implícitas, e a recorrência das soluções, que poderiam até mesmo dispensar as simulações. Além da confirmação de que é possível integrar simulações desde as primeiras fases, a contribuição principal do artigo é o mapeamento de processos entre projetista e simulador e sua intensidade para demonstrar as potencialidades e limitações das integrações, que podem ser úteis no desenvolvimento de interfaces de ferramentas e no treinamento de especialistas em simulação